# THIS FILE SHOULD BE OVER-RIDDEN IN YOUR SITE EXTENSION!
#   the exact code probably won't be useful, though you're welcome to modify and reuse
#   the current contents are mainly for testing and documentation

# set up some basic filters for use with products
#
# Each filter has two parts
#  * a parametrized named scope which expects a list of labels 
#  * an object which describes/defines the filter
#
# The filter description has three components
#  * a name, for displaying on pages
#  * a named scope which will 'execute' the filter
#  * a mapping of presentation labels to the relevant condition (in the context of the named scope)
#  * an optional list of labels and values (for use with object selection - see taxons examples below)
#
# The named scopes here have a suffix '_any', following SearchLogic's convention for a 
# scope which returns results which match any of the inputs. This is purely a convention,
# but might be a useful reminder. 
#
# When creating a form, the name of the checkbox group for a filter F should be 
# the name of F's scope with [] appended, eg "price_range_any[]", and for 
# each label you should have a checkbox with the label as its value. On submission,
# Rails will send the action a hash containing (among other things) an array named
# after the scope whose values are the active labels. 
#
# SearchLogic will then convert this array to a call to the named scope with the array
# contents, and the named scope will build a query with the disjunction of the conditions
# relating to the labels, all relative to the scope's context. 
#
# The details of how/when filters are used is a detail for specific models (eg products 
# or taxons), eg see the taxon model/controller.

# See specific filters below for concrete examples.


module ProductFilters

  # Example: filtering by price
  #   The named scope just maps incoming labels onto their conditions, and builds the conjunction
  #   'price' is in the base scope's context (ie, "select foo from products where ...") so
  #     we can access the field right away
  #   The filter identifies which scope to use, then sets the conditions for each price range
  #
  Product.scope :price_range_any,
    lambda {|opts| 
      conds = opts.map {|o| ProductFilters.price_filter[:conds][o]}.reject {|c| c.nil?}
      Product.scoped(:joins => :master).conditions_any(conds).scope :find
    }

  def ProductFilters.price_filter
    conds = [ [ "Under $10",    "price             <= 10" ],
              [ "$10 - $15",    "price between 10 and 15" ],
              [ "$15 - $18",    "price between 15 and 18" ],
              [ "$18 - $20",    "price between 18 and 20" ],
              [ "$20 or over",  "price             >= 20" ] ]
    { :name   => "Price Range",
      :scope  => :price_range_any,
      :conds  => Hash[*conds.flatten],
      :labels => conds.map {|k,v| [k,k]}
    }
  end


  # Example: filtering by possible brands
  # 
  # First, we define the scope. Two interesting points here: (a) we run our conditions
  #   in the scope where the info for the 'brand' property has been loaded; and (b) 
  #   because we may want to filter by other properties too, we give this part of the 
  #   query a unique name (which must be used in the associated conditions too).
  #
  # Secondly, the filter. Instead of a static list of values, we pull out all existing 
  #   brands from the db, and then build conditions which test for string equality on
  #   the (uniquely named) field "p_brand.value". There's also a test for brand info
  #   being blank: note that this relies on with_property doing a left outer join 
  #   rather than an inner join. 

  if Property.table_exists? && @@brand_property = Property.find_by_name("brand")
    Product.scope :brand_any,
      lambda {|opts| 
        conds = opts.map {|o| ProductFilters.brand_filter[:conds][o]}.reject {|c| c.nil?} 
        Product.with_property(@@brand_property, "p_brand").conditions_any(conds).scope(:find)
      } 

    def ProductFilters.brand_filter
      brands = ProductProperty.find_all_by_property_id(@@brand_property).map(&:value).uniq
      conds  = Hash[*brands.map {|b| [b, "p_brand.value = '#{b}'"]}.flatten]
      conds["No brand"] = "p_brand.value is NULL"
      { :name   => "All Brands",
        :scope  => :brand_any,
        :conds  => conds,
        :labels => (brands.sort + ["No brand"]).map {|k| [k,k]}
      }
    end
  end

  # Example: a parametrized filter
  #   The filter above may show brands which aren't applicable to the current taxon,
  #   so this one only shows the brands that are relevant to a particular taxon and 
  #   its descendents.
  #
  #   We don't have to give a new scope since the conditions here are a subset of the 
  #   more general filter, so decoding will still work - as long as the filters on a 
  #   page all have unique names (ie, you can't use the two brand filters together 
  #   if they use the same scope). To be safe, the code uses a copy of the scope.
  #
  #   HOWEVER: what happens if we want a more precise scope?  we can't pass 
  #   parametrized scope names to SearchLogic, only atomic names, so couldn't ask 
  #   for taxon T's customized filter to be used. BUT: we can arrange for the form 
  #   to pass back a hash instead of an array, where the key acts as the (taxon) 
  #   parameter and value is its label array, and then get a modified named scope
  #   to get its conditions from a particular filter. 
  #
  #   The brand-finding code can be simplified if a few more named scopes were added to 
  #   the product properties model. 

  if Property.table_exists? && @@brand_property 
    Product.scope :selective_brand_any, lambda {|opts| Product.brand_any(opts).scope(:find) }

    def ProductFilters.selective_brand_filter(taxon = nil)
      if taxon.nil? 
        taxon = Taxonomy.first.root 
      end 
      all_brands = ProductProperty.find_all_by_property_id(@@brand_property).map(&:value).uniq
      scope = ProductProperty.scoped(:conditions => ["property_id = ?", @@brand_property]).
                              scoped(:joins      => {:product => :taxons}, 
                                     :conditions => ["taxons.id in (?)", [taxon] + taxon.descendents])
      brands = scope.map {|p| p.value}

      { :name   => "Applicable Brands",
        :scope  => :selective_brand_any,
        :conds  => Hash[*all_brands.map {|m| [m, "p_colour.value like '%#{m}%'"]}.flatten],
        :labels => brands.sort.map {|k| [k,k]}
      }
    end
  end


  # Provide filtering on the immediate children of a taxon
  # 
  # This doesn't fit the pattern of the examples above, so there's a few changes.
  # Firstly, it uses an existing scope which was not built for filtering - and so 
  # has no need of a conditions mapping, and secondly, it has a mapping of name 
  # to the argument type expected by the other scope. 
  #
  # This technique is useful for filtering on objects (by passing ids) or with a 
  # scope that can be used directly (eg. testing only ever on a single property).
  # 
  # This scope selects products in any of the active taxons or their children.
  # 
  def ProductFilters.taxons_below(taxon)
    return ProductFilters.all_taxons if taxon.nil?
    { :name   => "Taxons under " + taxon.name,
      :scope  => :taxons_id_in_tree_any,
      :labels => taxon.children.sort_by(&:position).map {|t| [t.name, t.id]},
      :conds  => nil
    }
  end

  # Filtering by the list of all taxons
  #
  # Similar idea as above, but we don't want the descendents' products, hence
  # it uses one of the auto-generated scopes from SearchLogic.
  #
  # idea: expand the format to allow nesting of labels?
  def ProductFilters.all_taxons
    taxons = Taxonomy.all.map {|t| [t.root] + t.root.descendents }.flatten
    { :name   => "All taxons",
      :scope  => :taxons_id_equals_any,
      :labels => taxons.sort_by(&:name).map {|t| [t.name, t.id]},
      :conds  => nil	# not needed
    }
  end
end